Method for producing secondary battery

ABSTRACT

A method for producing a secondary battery including an electrode body having a positive electrode plate and a negative electrode plate, a prismatic outer body having an opening and houses the electrode body, a sealing plate that seals the opening of the prismatic outer body, and a positive electrode external terminal that is electrically connected to the positive electrode plate and attached to the sealing plate. The method includes a fixation step of electrically connecting a first positive electrode current collector to a positive electrode external terminal and fixing the first positive electrode current collector to the sealing plate, a first connection step of weld-connecting a stack of a plurality of positive electrode tabs to the second positive electrode current collector, and a second connection step of weld-connecting the first positive electrode current collector to the second positive electrode current collector after the fixation step and the first connection step.

TECHNICAL FIELD

The present invention relates to a method for producing a secondarybattery.

BACKGROUND ART

Prismatic secondary batteries, such as alkaline secondary batteries andnon-aqueous electrolyte secondary batteries, are used as driving powersources for electric vehicles (EVs), hybrid electric vehicles (HEVs,PHEVs), and other vehicles.

In such a prismatic secondary battery, a battery case includes abottomed, cylindrical prismatic outer body having an opening, and asealing plate that seals the opening. The battery case houses, togetherwith an electrolyte, an electrode body including a positive electrodeplate, a negative electrode plate, and separator. A positive electrodeterminal and a negative electrode terminal are attached to the sealingplate. The positive electrode terminal is electrical connected to thepositive electrode plate with a positive electrode current collectorinterposed therebetween. The negative electrode terminal is electricallyconnected to the negative electrode plate with a negative electrodecurrent collector interposed therebetween.

The positive electrode plate includes a positive electrode core made ofmetal and a positive electrode active material mixture layer formed onthe surface of the positive electrode core. A positive electrodecore-exposed portion without the positive electrode active materialmixture layer is formed on part of the positive electrode core. Apositive electrode current collector is connected to the positiveelectrode core-exposed portion. The negative electrode plate includes anegative electrode core made of metal and a negative electrode activematerial mixture layer formed on the surface of the negative electrodecore. A negative electrode core-exposed portion without the negativeelectrode active material mixture layer is formed on part of thenegative electrode core. A negative electrode current collector isconnected to the negative electrode core-exposed portion.

For example, Patent Literature 1 proposes a prismatic secondary batteryincluding a wound electrode body having a wound positive electrodecore-exposed portion in one end part and having a wound negativeelectrode core-exposed portion in the other end part. Patent Literature2 proposes a prismatic secondary battery including an electrode bodyhaving a positive electrode core-exposed portion and a negativeelectrode core-exposed portion in one end part.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Published Unexamined Patent ApplicationNo. 2009-032640

Patent Literature 2: Japanese Published Unexamined Patent ApplicationNo. 2008-226625

SUMMARY OF INVENTION Technical Problem

For secondary batteries for use in vehicles, particularly, secondarybatteries for use in EVs, PHEVs, and other vehicles, there is a need todevelop secondary batteries having a high volumetric energy density anda large battery capacity. In the case of the prismatic secondary batterydisclosed in Patent Literature 1, a battery case needs to contain leftand right spaces used to dispose the wound positive electrodecore-exposed portion and the wound negative electrode core-exposedportion, and an upper space between a sealing plate and the woundelectrode body. These spaces impose a difficulty in increasing thevolumetric energy density of secondary batteries.

Like the prismatic secondary battery disclosed in Patent Literature 2,the use of the electrode body including the positive electrodecore-exposed portion and the negative electrode core-exposed portion inone end part makes it easy to provide a prismatic secondary batteryhaving a high volumetric energy density.

The present invention is directed to a highly reliable secondary batteryhaving a high volumetric energy density.

Solution to Problem

A method for producing a secondary battery according to an aspect of thepresent invention is a method for producing a secondary batteryincluding:

an electrode body that includes a positive electrode plate and anegative electrode plate;

an outer body that has an opening and houses the electrode body;

a sealing plate that seals the opening;

an external terminal that is attached to the sealing plate;

a tab that is provided in the positive electrode plate or the negativeelectrode plate; and

a first current collector and a second current collector thatelectrically connect the tab to the external terminal.

The method includes:

a fixation step of electrically connecting the first current collectorto the external terminal and fixing the first current collector to thesealing plate;

a first connection step of weld-connecting a stack of a plurality of thetabs to the second current collector; and

a second connection step of connecting the first current collector tothe second current collector after the fixation step and the firstconnection step.

According to the above-described features, there is provided a highlyreliable secondary battery having a high volumetric energy density sincea stack of a plurality of the tabs can stably and strongly beweld-connected to the second current collector. Here, either one of thefixation step and the first connection step may be performed first.

Advantageous Effects of Invention

According to the present invention, there is provided a highly reliablesecondary battery having a high volumetric energy density.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a prismatic secondary battery accordingto an embodiment.

FIG. 2 is a sectional view taken along line II-II in FIG. 1.

FIG. 3 is a plan view of a positive electrode plate according to anembodiment.

FIG. 4 is a plan view of a negative electrode plate according to anembodiment.

FIG. 5 is a plan view of an electrode body element according to anembodiment.

FIG. 6 is a bottom view of a sealing plate to which each component hasbeen attached.

FIG. 7 is a sectional view taken along line VII-VII in FIG. 6.

FIG. 8 is an enlarged view illustrating the first positive electrodecurrent collector, the second positive electrode current collector, thecurrent interrupting mechanism, and the surrounding area in FIG. 7.

FIG. 9 is an enlarged view illustrating the first negative electrodecurrent collector, the second negative electrode current collector, andthe surrounding area in FIG. 7.

FIG. 10 is a view illustrating the process of connecting tabs to secondcurrent collectors.

FIG. 11 is a sectional view illustrating the process of connecting thetabs to the second current collectors.

FIG. 12 is a sectional view in the longitudinal direction of the sealingplate after the second positive electrode current collector is connectedto the first positive electrode current collector and the secondnegative electrode current collector is connected to the first negativeelectrode current collector.

FIG. 13 is a bottom view of a sealing plate to which each component hasbeen attached in a prismatic secondary battery according to Modification1.

FIG. 14 is a view illustrating the process of connecting tabs to secondcurrent collectors in the prismatic secondary battery according toModification 1.

FIG. 15 is a bottom view of a sealing plate to which each component hasbeen attached in a prismatic secondary battery according to Modification2.

FIG. 16 is a sectional view in the longitudinal direction of the sealingplate to which each component has been attached in the prismaticsecondary battery according to Modification 2.

FIG. 17 is an enlarged view illustrating the first positive electrodecurrent collector, the second positive electrode current collector, thecurrent interrupting mechanism, and the surrounding area in FIG. 16.

DESCRIPTION OF EMBODIMENTS

The structure of a prismatic secondary battery 20 according to anembodiment will be described below. The present invention is not limitedto the following embodiment.

FIG. 1 is perspective view of the prismatic secondary battery 20. FIG. 2is a sectional view taken along line II-II in FIG. 1. As illustrated inFIG. 1 and FIG. 2, the prismatic secondary battery 20 has a battery case100. The battery case 100 includes a bottomed, cylindrical prismaticouter body 1 having an opening, and a sealing plate 2 that seals theopening of the prismatic outer body 1. The prismatic outer body 1 andthe sealing plate 2 are preferably each made of metal, and preferablymade of, for example, aluminum or an aluminum alloy. The prismatic outerbody 1 houses, together with an electrolyte, an electrode body 3including plural positive electrode plates and plural negative electrodeplates that are stacked with separators each interposed therebetween. Aninsulating sheet 14 is disposed between the electrode body 3 and theprismatic outer body 1.

A positive electrode tab 40 and a negative electrode tab 50 are disposedon an edge of the electrode body 3 adjacent to the sealing plate 2. Thepositive electrode tab 40 is electrically connected to a positiveelectrode external terminal 7 with a second positive electrode currentcollector 6 b and a first positive electrode current collector 6 ainterposed therebetween. The negative electrode tab 50 is electricallyconnected to a negative electrode external terminal 9 with a secondnegative electrode current collector 8 b and a first negative electrodecurrent collector 8 a interposed therebetween.

The positive electrode tab 40 is connected to a surface of the secondpositive electrode current collector 6 b adjacent to the electrode body3. The positive electrode tab 40 is being bent. This configurationprovides a secondary battery having a high volumetric energy density.The negative electrode tab 50 is connected to a surface of the secondnegative electrode current collector 8 b adjacent to the electrode body3. The negative electrode tab 50 is being bent. This configurationprovides a secondary battery having a high volumetric energy density.

The positive electrode external terminal 7 is fixed to the sealing plate2 with an external insulating member 11, which is made of resin,interposed therebetween. The negative electrode external terminal 9 isfixed to the sealing plate 2 with an external insulating member 13,which is made of resin, interposed therebetween. The positive electrodeexternal terminal 7 is preferably made of metal, and more preferablymade of aluminum or an aluminum alloy. The negative electrode externalterminal 9 is preferably made of metal, and more preferably made ofcopper or a copper alloy. More preferably, the negative electrodeexternal terminal 9 has a copper or copper alloy portion inside thebattery case 100 and has an aluminum or aluminum alloy portion outsidethe battery case 100. The negative electrode external terminal 9preferably has the surface coated with nickel or the like.

The conduction path between the positive electrode plate and thepositive electrode external terminal 7 is provided with a currentinterrupting mechanism 60. The current interrupting mechanism 60operates so as to interrupt the conduction path between the positiveelectrode plate and the positive electrode external terminal 7 when theinternal pressure of the battery case 100 reaches a predetermined valueor higher. The conduction path between the negative electrode plate andthe negative electrode external terminal 9 may be provided with acurrent interrupting mechanism.

The sealing plate 2 has a gas release valve 17. The gas release valve 17fractures when the internal pressure of the battery case 100 reaches apredetermined value or higher and releases gas in the battery case 100to the outside of the battery case 100. The operating pressure of thegas release valve 17 is set to a value larger than the operatingpressure of the current interrupting mechanism 60.

The sealing plate 2 has an electrolyte injection port 15. After anelectrolyte is injected into the battery case 100 through theelectrolyte injection port 15, the electrolyte injection port 15 issealed with a sealing plug 16.

Next, a method for producing the prismatic secondary battery 20 will bedescribed.

Production of Positive Electrode Plate

A positive electrode slurry containing a lithium-nickel-cobalt-manganesecomposite oxide as a positive electrode active material, polyvinylidenefluoride (PVdF) as a binder, a carbon material as a conductive agent,and N-methyl-2-pyrrolidone (NMP) as a dispersion medium is prepared. Thepositive electrode slurry is applied to each surface of an aluminumfoil. The aluminum foil has a rectangular shape and, a thickness of 15μm and functions as a positive electrode core. The positive electrodeslurry is dried to remove N-methyl-2-pyrrolidone in the positiveelectrode slurry, whereby a positive electrode active material mixturelayer is formed on the positive electrode core. The positive electrodeactive material mixture layer is then pressed into a predeterminedthickness. The resulting positive electrode plate is cut into apredetermined shape.

FIG. 3 is a plan view of a positive electrode plate 4 prepared by usingthe above-described method. As illustrated in FIG. 3, the positiveelectrode plate 4 has a body having a positive electrode active materialmixture layer 4 b on each surface of a rectangular positive electrodecore 4 a. The positive electrode plate 4 has the positive electrode tab40. The positive electrode core 4 a projects from an edge of the body,and the projecting positive electrode core 4 a constitutes the positiveelectrode tab 40. The positive electrode tab 40 may be a part of thepositive electrode core 4 a as illustrated in FIG. 3, or the positiveelectrode tab 40 may be formed by connecting another member to thepositive electrode core 4 a. Preferably, a part of the positiveelectrode tab 40 adjacent to the positive electrode active materialmixture layer 4 b has a positive electrode protective layer 4 d. Thepositive electrode protective layer 4 d has a larger electricalresistance than the positive electrode active material mixture layer 4b. The positive electrode protective layer 4 d preferably contains abinder and ceramic particles made of alumina, silica, zirconia, or otherceramics. The positive electrode protective layer 4 d more preferablycontains conductive particles made of a carbon material or othermaterials.

Production of Negative Electrode Plate

A negative electrode slurry containing graphite as a negative electrodeactive material, a styrene-butadiene rubber (SBR) as a binder,carboxymethylcellulose (CMC) as a thickener, and water is prepared. Thenegative electrode slurry is applied to each surface of a copper foil.The copper foil has a rectangular shape and a thickness of 8 μm andfunctions as a negative electrode core. The negative electrode slurry isdried to remove water in the negative electrode slurry, whereby anegative electrode active material mixture layer is formed on thenegative electrode core. The negative electrode active material mixturelayer is then pressed into a predetermined thickness. The resultingnegative electrode plate is cut into a predetermined shape.

FIG. 4 is a plan view of a negative electrode plate 5 prepared by usingthe above-described method. As illustrated in FIG. 4, the negativeelectrode plate 5 has a body having a negative electrode active materialmixture layer 5 b on each surface of a rectangular negative electrodecore 5 a. The negative electrode plate 5 has a negative electrode tab50. The negative electrode core 5 a projects from an edge of the body,and the projecting negative electrode core 5 a constitutes the negativeelectrode tab 50. The negative electrode tab 50 may be a part of thenegative electrode core 5 a as illustrated in FIG. 4, or the negativeelectrode tab 50 may be formed by connecting another member to thenegative electrode core 5 a.

Production of Electrode Body Element

Stacked electrode body elements (3 a, 3 b) are produced as follows:preparing 50 positive electrode plates 4 and 51 negative electrodeplates 5 by using the foregoing methods; and stacking the positiveelectrode plates 4 and the negative electrode plates 5 with rectangularpolyolefin separators each interposed therebetween. As illustrated inFIG. 5, the stacked electrode body elements (3 a, 3 b) are produced soas to include the stacked positive electrode tabs 4 of the positiveelectrode plates 4 and the stacked negative electrode tabs 50 ofnegative electrode plates 5 on one edge. The separator is located oneach outer surface of the electrode body elements (3 a, 3 b), theelectrode plates and the separators are fixed to each other with a tapeor the like such that they are stacked on top of one another.Alternatively, the separators may each have adhesive layers so that eachseparator adheres to a corresponding one of the positive electrodeplates 4 and each separator adheres to a corresponding one of thenegative electrode plates 5.

Preferably, the separators have the same size as the negative electrodeplates 5 or have a larger size than the negative electrode plates 5 inplan view. The positive electrode plate 4 and the negative electrodeplate 5 may be stacked on top of each other after the peripheries of twoseparators between which the positive electrode plate 4 is interposed ehot melted. To produce the electrode body elements (3 a, 3 b), theelectrode plate 4 and the negative electrode plate 5 can also be stackedon top of each other by using a long separator while the long separatoris bent in hairpin curves. Alternatively, the positive electrode plate 4and the negative electrode plate 5 can also be stacked on top of eachother by using a long separator while the long separator is wound.

Assembly of Sealing Body

With reference to FIG. 2, FIG. 6, FIG. 7, and FIG. 8, a method forattaching the positive electrode external terminal 7 and the firstpositive electrode current collector 6 a to the sealing plate 2, and thestructure of the current interrupting mechanism 60 will be described.

The external insulating member 11 is disposed on the outer surface sideof a positive electrode terminal attachment hole 2 a in the sealingplate 2, and an internal insulating member 10 and a cup-shapedconductive member 61 are disposed on the inner surface side of thepositive electrode terminal attachment hole 2 a. Next, the positiveelectrode external terminal 7 is inserted into the through-hole of theexternal insulating member 11, the positive electrode terminalattachment hole 2 a of the sealing plate 2, the through-hole of theinternal insulating member 10, and the through-hole of the conductivemember 61. The end of the positive electrode external terminal 7 iscrimped onto the conductive member 61. The positive electrode externalterminal 7, the external insulating member 11, the sealing plate 2, theinternal insulating member 10, and the conductive member 61 are fixedaccordingly. The crimped portion of the positive electrode externalterminal 7 is preferably welded to the conductive member 61 by means oflaser welding or the like. The internal insulating member 10 and theexternal insulating member 11 are preferably each made of resin.

The conductive member 61 has an opening adjacent to the electrode body3. A disc-shaped deformation plate 62 is placed so as to close theopening of the conductive member 61, and a peripheral portion of thedeformation plate 62 is weld-connected to the conductive member 61. Theopening of the conductive member 61 is sealed with the deformation plate62 accordingly. The conductive member 61 and the deformation plate 62are preferably each made of metal, and more preferably made of aluminumor an aluminum alloy. The opening of the conductive member 61 adjacentto the electrode body 3 does not necessarily have a circular shape, butmay have a rectangular shape. The deformation plate 62 is shaped so asto seal the opening of the conductive member 61.

Next, a first insulating member 63 made of resin is disposed on theelectrode body 3 side with respect to the deformation plate 62.Preferably, the first insulating member 63 has a connection part, andthe connection part is connected to the internal insulating member 10.Preferably, the first insulating member 63 has a claw-shaped hookfixation part, the conductive member 61 has a flange, a recess, or aprotrusion, and the hook fixation part of the first insulating member 63is fixed to the flange, the recess, or the protrusion of the conductivemember 61.

The first insulating member 63 has a fixation protrusion 63 a on itssurface adjacent to the electrode body 3. The first insulating member 63preferably has an insulating member first region 63 x disposed below thedeformation plate 62, an insulating member second region 63 y extendingfrom the end of the insulating member first region 63 x toward thesealing plate 2, and an insulating member third region 63 z horizontallyextending from the end of the insulating member second region 63 y. Theinsulating member third region 63 z has an insulating member opening 63b at a position facing the electrolyte injection port 15 of the sealingplate 2. An insulating member protrusion 63 c protruding toward theelectrode body 3 is disposed at the edge of the insulating memberopening 63 b.

Next, the first positive electrode current collector 6 a is disposed onthe electrode body 3 side with respect to the first insulating member63. The first positive electrode current collector 6 a has a fixationthrough-hole 6 d. The fixation protrusion 63 a of the first insulatingmember 63 is inserted into the fixation through-hole 6 d of the firstpositive electrode current collector 6 a, and the diameter of the end ofthe fixation protrusion 63 a is enlarged. As a result, the firstinsulating member 63 and the first positive electrode current collector6 a are fixed to each other. A fixation part 70 is formed accordingly.As illustrated in FIG. 6, four fixation parts 70 are preferably providedso as to surround the connection part between the deformation plate 62and the first positive electrode current collector 6 a.

The deformation plate 62 and the first positive electrode currentcollector 6 a are then weld-connected to each other through athrough-hole in the first insulating member 63. Preferably, the firstpositive electrode current collector 6 a has a thin portion 6 c, and thethin portion 6 c is preferably weld-connected to the deformation plate62. Preferably, the thin portion 6 c has an opening at its center, and aperipheral portion of the opening is weld-connected to the deformationplate 62. The thin portion 6 c more preferably has an annular notch thatsurrounds the connection part between the deformation plate 62 and thefirst positive electrode current collector 6 a. The first insulatingmember 63 and the first positive electrode current collector 6 a may beconnected to each other in advance, and the first insulating member 63connected to the first positive electrode current collector 6 a may bedisposed on the electrode body 3 side with respect to the deformationplate 62.

When the internal pressure of the battery case 100 reaches apredetermined value or higher, the deformation plate 62 deforms suchthat a central portion of the deformation plate 62 moves upward (towardthe positive electrode external terminal 7). The thin portion 6 c of thefirst positive electrode current collector 6 a fractures upondeformation of the deformation plate 62. The fracture causesdisconnection of the conduction path between the positive electrodeplate 4 and the positive electrode external terminal 7.

The leak inspection on the connection part between the conductive member61 and the deformation plate 62 can be carried out by supplying gas tothe inside of the current interrupting mechanism 60 through a terminalthrough-hole 7 b formed in the positive electrode external terminal 7.While the gas causes the deformation plate 62 to push against the firstpositive electrode current collector 6 a, the deformation plate 62 andthe first positive electrode current collector 6 a can be weld-connectedto each other. Finally, the terminal through-hole 7 b is sealed with aterminal sealing member 7 a. The terminal sealing member 7 a preferablyincludes a metal plate 7 x and a rubber member 7 y.

The first positive electrode current collector 6 a has a currentcollector first region 6 a 1 disposed below the deformation plate 62, acurrent collector second region 6 a 2 extending from an end of thecurrent collector first region 6 a 1 toward the sealing plate 2, and acurrent collector third region 6 a 3 horizontally extending from anupper end of the current collector second region. The current collectorthird region 6 a 3 has a current collector protrusion 6 x on its surfaceadjacent to the electrode body 3.

The current collector first region 6 a 1 of the first positive electrodecurrent collector 6 a is disposed so as to face the insulating memberfirst region 63 x of the first insulating member 63. The currentcollector second region 6 a 2 of the first positive electrode currentcollector 6 a is disposed so as to face the insulating member secondregion 63 y of the first insulating member 63. The current collectorthird region 6 a 3 of the first positive electrode current collector 6 ais disposed so as to face the insulating member third region 63 z of thefirst insulating member 63.

With reference to FIG. 2, FIG. 6, FIG. 7, and FIG. 9, a method forattaching the negative electrode external terminal 9 and the firstnegative electrode current collector 8 a to the sealing plate 2 will bedescribed.

The external insulating member 13 is disposed on the outer surface sideof a negative electrode terminal attachment hole 2 b in the sealingplate 7 and an internal insulating member 12 and the first negativeelectrode current collector 8 a are disposed on the inner surface sideof the negative electrode terminal attachment hole 7 b. Next, thenegative electrode external terminal 9 is inserted into the through-holeof the external insulating member 13, the negative electrode terminalattachment hole 2 b of the sealing plate 2, the through-hole of theinternal insulating member 12, and the through-hole of the firstnegative electrode current collector 8 a. The end of the negativeelectrode external terminal 9 is crimped onto the first negativeelectrode current collector 8 a. The external insulating member 13, thesealing plate 2, the internal insulating member 12, and the firstnegative electrode current collector 8 a are fixed accordingly. Thecrimped portion of the negative electrode external terminal 9 ispreferably weld-connected to the first negative electrode currentcollector 8 a by means of laser welding or the like. The internalinsulating member 12 and the external insulating member 13 arepreferably each made of resin.

Connection between Second Current Collector and Tabs

FIG. 10 is a illustrating a method for connecting the positive electrodetabs 40 (40 a, 40 b) to the second positive electrode current collector6 b, and a method for connecting the negative electrode tabs 50 (50 a,50 b) to the second negative electrode current collector 8 b. Twoelectrode body elements are produced by using the above-described methodand defined as a first electrode body element 3 a and a second electrodebody element 3 b. The first electrode body element 3 a and the secondelectrode body element 3 b may have the completely same structure or mayhave different structures.

The second positive electrode current collector 6 b and the secondnegative electrode current collector 6 b are disposed between the firstelectrode body element 3 a and the second electrode body element 3 b.The stacked positive electrode tabs 40 a protruding from the firstelectrode body element 3 a are disposed on the second positive electrodecurrent collector 6 b. The stacked negative electrode tabs 50 aprotruding from the first electrode body element 3 a are disposed of thesecond negative electrode current collector 8 b. The stacked positiveelectrode tabs 40 b protruding from the second electrode body element 3b are disposed on the second positive electrode current collector 6 b.The stacked negative electrode tabs 50 b protruding from the secondelectrode body element 3 b are disposed on the second negative electrodecurrent collector 8 b. The positive electrode tabs 40 a and the positiveelectrode tabs 40 b are weld-connected to the second positive electrodecurrent collector 6 b to form weld-connected parts 90. The negativeelectrode tabs 50 a and the negative electrode tabs 50 b areweld-connected to the second negative electrode current collector 8 b toform weld-connected parts 90. Weld connection is preferably performed inthe following manner.

As illustrated in FIG. 11, the tabs (the positive electrode tabs 40 a or40 b, the negative electrode tabs 50 a or 50 b) and the currentcollector (the second positive electrode current collector 6 b, thesecond negative electrode current collector 8 b) are sandwiched betweenwelding jigs 95 from above and below. In this state, welding isperformed. The welding method is preferably ultrasonic welding orresistance welding. Such welding ensures weld connection between. thestacked tabs and the current collector. In the case where many tabs arestacked, for example, in the case where 20 or more tabs are stacked,ultrasonic welding or resistance welding can form more reliableweld-connected parts than laser welding or the like because ultrasonicwelding or resistance welding can be performed with the tabs and thecurrent collector sandwiched between a pair of welding jigs 95. Inresistance welding, the pair of welding jigs 95 is a pair of resistancewelding electrodes. In ultrasonic welding, the pair of welding jigs 95correspond to a horn and an anvil.

The positive electrode tabs 40 a of the first. electrode body element 3a are connected to one side of the second positive electrode currentcollector 6 b with respect to a central portion of the second positiveelectrode current collector 6 b in the width direction. The positiveelectrode tabs 40 b of the second electrode body element 3 b areconnected to the other side of the second positive electrode currentcollector 6 b with respect to a central portion of the second positiveelectrode current collector 6 b in the width direction.

The negative electrode tabs 50 a of the first electrode body element 3 aare connected to one side of the second negative electrode currentcollector 8 b with respect to a central portion of the second negativeelectrode current collector 8 b in the width direction. The negativeelectrode tabs 50 b of the second electrode body element 3 b areconnected to the other side of the second negative electrode currentcollector 8 b with respect to a central portion of the second negativeelectrode current collector 8 b in the width direction.

As illustrated in FIG. 10, the second positive electrode currentcollector 6 b has an opening 6 z. After the second positive electrodecurrent collector 6 b is connected to the first positive electrodecurrent collector 6 a, the opening 6 z is placed at a positioncorresponding to the electrolyte injection port 15 of the sealing plate2. The positive electrode tabs 40 a of the first electrode body element3 a are connected to one side of the second positive electrode currentcollector 6 b with respect to the opening 6 z in the width direction ofthe second positive electrode current collector 6 b. The positiveelectrode tabs 40 b of the second electrode both element 3 are connectedto the other side of the second positive electrode current collector 6 bwith respect to the opening 6 z the width direction of the secondpositive electrode current collector 6 b. As the second positiveelectrode current collector 6 b, the positive electrode tabs 40 a, andthe positive electrode tabs 40 b are viewed in the directionperpendicular to the sealing plate 2, portions of the positive electrodetabs 40 a and the positive electrode tabs 40 b substantially parallel tothe second positive electrode current collector 6 b preferably do notoverlap the opening 6 z. This configuration can avoid the secondpositive electrode current collector 6 b or the positive electrode tabs40 a and the positive electrode tabs 40 b from interfering withinjection of an electrolyte.

Here, either one of the following steps may be performed first: afixation step of fixing the first positive electrode current collector 6a and the first negative electrode current collector 8 a to the sealingplate 2; and a connection step of respectively connecting the positiveelectrode tabs 40 and the negative electrode tabs 50 to the secondpositive electrode current collector 6 b and the second negativeelectrode current collector 8 b. Preferably, after the positiveelectrode tabs are connected to the second positive electrode currentcollector and the negative electrode tabs are connected to the secondnegative electrode current collector, the second positive electrodecurrent collector is connected to the first positive electrode currentcollector, and the second negative electrode current collector isconnected to the first negative electrode current collector.

Connection between First Positive Electrode Current Collector and SecondPositive Electrode Current Collector

As illustrated in FIG. 6 and FIG. 7, the first positive electrodecurrent collector 6 a has a current collector protrusion 6 x. Asillustrated in FIG. 10, the second positive electrode current collector6 b has a current collector opening 6 y. As illustrated in FIGS. 7 and8, the second positive electrode current collector 6 b is placed on theinsulating member third region 63 z of the first insulating member 63such that the current collector protrusion 6 x of the first positiveelectrode current collector 6 a is positioned in the current collectoropening 6 y of the second positive electrode current collector 6 b. Thecurrent collector protrusion 6 x of the first positive electrode currentcollector 6 a is welded to the edge of the current collector opening 6 yof the second positive electrode current collector 6 b by means ofirradiation with an energy ray, such as a laser. The first positiveelectrode current collector 6 a and the second positive electrodecurrent collector 6 b are connected each other accordingly. The secondpositive electrode current collector 6 b has current collector firstrecess 6 f around the current collector opening 6 y. In other words, thecurrent collector opening 6 y is formed at the center of the currentcollector first recess 6 f. The first positive electrode currentcollector 6 a and the second positive electrode current collector 6 bare weld-connected to each other at the current collector first recess 6f. When the current collector first recess 61 is formed around thecurrent collector opening 6 y, the first positive electrode currentcollector 6 a and the second positive electrode current collector 6 bcan be weld-connected to each other without increasing the height of thecurrent collector protrusion 6 x.

As illustrated in FIG. 8, the second positive electrode currentcollector 6 b has a tab connection region 6 b 1 to which the positiveelectrode tabs 40 are connected, and a current collector connectionregion 6 b 2 to which the first positive electrode current collector 6 ais connected. A stepped part 6A is formed between the tab connectionregion 6 b 1 and the current collector connection region 6 b 2. In thedirection perpendicular to the sealing plate 2, the distance between thesealing plate 2 and the tab connection region 6 b 1 is smaller than thedistance between the sealing plate 2 and the current collectorconnection region 6 b 2. Such a configuration results in a small spaceoccupied by the current collection part and provides a secondary batteryhaving a high volumetric energy density. The tab connection region 6 b 1is preferably disposed substantially parallel (e.g., at an angle of ±20°or less) to the sealing plate 2.

As illustrated in FIG. 10, the second positive electrode currentcollector 6 b has target holes 6 e on both sides of the currentcollector opening 6 y. During welding between the first positiveelectrode current collector 6 a and the second positive electrodecurrent collector 6 b by means of irradiation with an energy ray, suchas a laser, the target holes 6 e are preferably used as targets forimage correction. Preferably, position correction is performed bydetecting the target holes 6 e on the image, and irradiation with energyrays is performed along the shape of the current collector opening 6 y.Each target hole 6 e may be a recess instead of a through-hole. The areaof each target hole 6 e in plan view is preferably smaller than the areaof the current collector opening 6 y in plan view. In the widthdirection of the second positive electrode current collector 6 b, thecurrent collector opening 6 y is preferably aligned with the targetholes 6 e.

As illustrated in FIG. 8, a current collector second recess 6 w isformed in a surface of the first positive electrode current collector 6a that faces the first insulating member 63 and that is located on theback side of the current collector protrusion 6 x. This configuration ispreferred because it is easy to form a large weld-connected part betweenthe first positive electrode current collector 6 a and the secondpositive electrode current collector 6 b. The formation of the currentcollector second recess 6 w can protect the first insulating member fromdamage caused by welding heat during weld connection between the firstpositive electrode current collector 6 a and the second positiveelectrode current collector 6 b.

As illustrated in FIG. 8 the lower end (the end adjacent to theelectrode body 3) of the insulating member protrusion 63 c of the firstinsulating member 63 preferably protrudes downward (toward the electrodebody 3) beyond the lower surface of the second positive electrodecurrent collector 6 b around the opening 6 z. This configuration canassuredly avoid contact between the sealing plug 16 and the secondpositive electrode current collector 6 b. Such contact is effectivelyavoided when the sealing plug 16 that seals the electrolyte injectionport 15 in the sealing plate 2 protrudes downward (toward the electrodebody 3) beyond the lower surface of the sealing plate 2. The insulatingmember protrusion 63 c preferably has an annular shape. However, theinsulating member protrusion 63 c does not necessarily have an annularshape and may have a partially cut annular shape.

The second positive electrode current collector 6 b has the opening 6 zat a position facing the electrolyte injection port 15 formed thesealing plate 2. The insulating member third region 63 z of the firstinsulating member 63 preferably has a fixation part to be fixed to thesecond positive electrode current collector 6 b. For example, aclaw-shaped fixation part can be formed in the first insulating member63 and can be hooked on and fixed to the second positive electrodecurrent collector 6 b. Alternatively, the first insulating member 63 maybe fixed to the second positive electrode current collector 6 b asfollows: forming a protrusion in the first insulating member 63; formingan opening or cut for fixation the second positive electrode currentcollector 6 b; inserting the protrusion of the first insulating member63 into the opening or cut for fixation in the second positive electrodecurrent collector 6 b; and enlarging the diameter of the end of theprotrusion of the first insulating member 63.

As illustrated in FIG. 8, the insulating member first region 63 x of thefirst insulating member 63 is disposed so as to face the currentcollector first region 6 a 1 of the first positive electrode currentcollector 6 a. The insulating member second region 63 y of the firstinsulating member 63 is disposed so as to face the current collectorsecond region 6 a 2 of the first positive electrode current collector 6a. This configuration can assuredly avoid formation of a conduction pathbetween the first positive electrode current collector 6 a and thedeformation plate 62 or between the first positive electrode currentcollector 6 a and the conductive member 61 after the currentinterrupting mechanism 60 operates to disconnect electrical connectionbetween the first positive electrode current collector 6 a and thedeformation plate 62.

Connection between First Negative Electrode Current Collector and SecondNegative Electrode Current Collector

As illustrated in FIG. 6 and FIG. 7, the first negative electrodecurrent collector 8 a has a current collector protrusion 8 x. Asillustrated in FIG. 9 and FIG. 12, the second negative electrode currentcollector 8 b has a current collector opening 8 y. As illustrated inFIG. 12, the second negative electrode current collector 8 b is placedon the internal insulating member 12 such that the current collectorprotrusion 8 x of the first negative electrode current collector 8 a ispositioned in the current collector opening 8 y of the second negativeelectrode current collector 8 b. The current collector protrusion 8 x ofthe first negative electrode current collector 8 a is welded to the edgeof the current collector opening 8 y of the second negative electrodecurrent collector 8 b by means of irradiation with an energy ray, suchas a laser. The first negative electrode current collector 8 a and thesecond negative electrode current collector 8 b are connected to eachother accordingly. The second negative electrode current collector 8 bhas a current collector first recess 8 f around the current collectoropening 8 y. In other words, the current collector opening 8 y is formedat the center of the current collector first recess 8 f. The firstnegative electrode current collector 8 a and the second negativeelectrode current collector 8 b are weld-connected to each other at thecurrent collector first recess 8 f. Like the second positive electrodecurrent collector 6 b, the second negative electrode current collector 8b has target holes 8 e.

The first negative electrode current collector 8 a and the secondnegative electrode current collector 8 b are preferably made of copperor a copper alloy. The first negative electrode current collector 8 aand the second negative electrode current collector 8 b each preferablyhave a nickel layer on their surfaces. A nickel layer is preferablyformed on the surface of the current collector protrusion 8 x of thefirst negative electrode current collector 8 a. A nickel layer ispreferably formed on the surface of the second negative electrodecurrent collector 8 b at the edge of the current collector opening 8 y.

As illustrated in FIG. 9, a current collector second recess 8 w isformed in a surface of the first negative electrode current collector 8a that faces the internal insulating member 12 and that is located onthe back side of the current collector protrusion 8 x. Thisconfiguration is preferred because it is easy to form a largeweld-connected part between the first negative electrode currentcollector 8 a and the second negative electrode current collector 8 b.The formation of the current collector second recess 8 w can protect theinternal insulating member 12 from damage caused by welding heat duringweld connection between the first negative electrode current collector 8a and the second negative electrode current collector 8 b.

As illustrated in FIG. 9, the second negative electrode currentcollector 8 b has a tab connection region 8 b 1 to which the negativeelectrode tabs 50 are connected, and a current collector connectionregion 8 b 2 to which the first negative electrode current collector 8 ais connected. A stepped part 8A is formed between the tab connectionregion 8 b 1 and the current collector connection region 8 b 2. In thedirection perpendicular to the sealing plate 2, the distance between thesealing plate 2 and the tab connection region 8 b 1 is smaller than thedistance between the sealing plate 2 and the current collectorconnection region 8 b 2. Such a configuration results in a small spaceoccupied by the current collection part and provides a secondary batteryhaving a high volumetric energy density.

The internal insulating member 12 preferably has a fixation part to befixed to the second negative electrode current collector 8 b. Forexample, a claw-shaped fixation part can be formed in the internalinsulating member 12 and can be hooked on and fixed to the secondnegative electrode current collector 8 b. Alternatively, the internalinsulating member 12 may be fixed to the second negative electrodecurrent collector 8 b as follows: forming a protrusion in the internalinsulating member 12; forming an opening or cut for fixation in thesecond negative electrode current collector 8 b; inserting theprotrusion of the internal insulating member 12 into the opening or cutfor fixation in the second negative electrode current collector 8 b; andenlarging the diameter of the end of the protrusion of the internalinsulating member 12.

Since the shape of the current collector protrusion 6 x in the firstpositive electrode current collector 6 a is different from the shape ofthe current collector protrusion 8 x the first negative electrodecurrent collector 8 a, this configuration can assuredly avoid accidentalconnection between the first positive electrode current collector 6 aand the second negative electrode current collector 8 b or between thefirst negative electrode current collector 8 a and the second positiveelectrode current collector 6 b.

The current collector protrusion 6 x in the first positive electrodecurrent collector 6 a is formed such that the major axis of the currentcollector protrusion 6 x extends in the transverse direction of thesealing plate 2. The current collector protrusion 8 x in the firstnegative electrode current collector 8 a is formed such that the majoraxis of the current collector protrusion 8 x extends in the longitudinaldirection of the sealing plate 2. Such a configuration can absorb adifference between the center-to-center distance between the currentcollector protrusion 6 x in the first positive electrode currentcollector 6 a and the current collector protrusion 8 x in the firstnegative electrode current collector 8 a and the center-to-centerdistance between the current collector opening 6 y in the secondpositive electrode current collector 6 b and the electrode currentcollector opening 8 y in the second negative electrode current collector8 b. This configuration can avoid the possibility of assembly defects inthe case of positioning both on the positive electrode side and thenegative electrode side and the possibility of low positional accuracydue to a failure of positioning on one electrode side in the case ofpositioning on the other electrode side.

The shape of the current collector protrusion 6 x in the first positiveelectrode current collector 6 a is preferably different from the shapeof the current collector protrusion 8 x in the first negative electrodecurrent collector 8 a. The current collector protrusion 6 x and thecurrent collector protrusion 8 x preferably have a non-perfect circularshape and preferably have a rectangular shape, an elliptical shape, or atrack shape.

In the case where one of the current collector protrusion 6 x in thefirst positive electrode current collector 6 a and the current collectorprotrusion 8 x in the first negative electrode current collector 8 a hasa major axis direction different from that of the other, the currentinterrupting mechanism is preferably provided on the positive electrodeside, the major axis of the current collector protrusion 6 x in thefirst positive electrode current collector 6 a preferably extends in thetransverse direction of the sealing plate 2, and the major axis of thecurrent collector protrusion 8 x in the first negative electrode currentcollector 8 a preferably extends in the longitudinal direction of thesealing plate 2. This configuration can reduce a space occupied by thecurrent collection part.

Production of Electrode Body

The positive electrode tabs 40 a, the positive electrode tabs 40 b, thenegative electrode tabs 50 a, and the negative electrode tabs 50 b arebent such that the upper surface of the first electrode body element 3 aand the upper surface of the second electrode body element 3 b in FIG.10 comes into contact with each other. Accordingly, the first electrodebody element 3 a and the second electrode body element 3 b are combinedtogether into one electrode body 3.

Assembly of Prismatic Secondary Battery

The electrode body 3 attached to the sealing plate 2 is covered with theinsulating sheet 14 and inserted into the prismatic outer body 1. Theinsulating sheet 14 is preferably formed by bending a flat insulatingsheet in a box shape or bag shape. The opening of the prismatic outerbody 1 is closed by joining the sealing plate 2 and the prismatic outerbody 1 by means of laser welding or the like. Subsequently, anon-aqueous electrolyte containing an electrolyte solvent and anelectrolyte salt is injected through the electrolyte injection port 15provided in the sealing plate 2. The electrolyte injection port 15 issealed with the sealing plug 16.

Method for Producing Prismatic Secondary Battery

The above-described method can reduce the proportion of a space occupiedby the current collection part including the positive electrode tabs 40,the first positive electrode current collector 6 a, the second positiveelectrode current collector 6 b, the negative electrode tabs 50, thefirst negative electrode current collector 8 a, the second negativeelectrode current collector 8 b, and other components, and can provide asecondary battery having a high volumetric energy density. According tothe above-described configuration, there is provided a highly reliablesecondary battery since a stack of a plurality of the tabs can stablyand strongly be weld-connected to the second current collector.

Modification 1

FIG. 13 is a bottom view of a sealing plate to which each component hasbeen attached in a prismatic secondary battery according toModification 1. FIG. 14 is a view illustrating the process connectingtab to second current collectors in the prismatic secondary batteryaccording to Modification 1. The prismatic secondary battery accordingto Modification 1 differs from the prismatic secondary battery 20according to the embodiment in the shapes of the first negativeelectrode current collector and the second negative electrode currentcollector.

In the prismatic secondary battery according to Modification 1, acurrent collector protrusion 108 x in a first negative electrode currentcollector 108 a is formed such that the major axis of the currentcollector protrusion 108 x extends in the transverse direction of thesealing plate 2. In the prismatic secondary battery according toModification 1, a current collector opening 108 y in a second negativeelectrode current collector 108 b is formed such that the major axis ofthe current collector opening 108 y extends the transverse direction ofthe sealing plate 2. This configuration can further reduce a spaceoccupied by the current collecting part.

The second negative electrode current collector 108 b has a currentcollector first recess 108 f around the current collector opening 108 y.Like the second negative electrode current collector 8 b, the secondnegative electrode current collector 108 b has target holes 108 e. Acurrent collector second recess 108 w is formed in a surface of thefirst negative electrode current collector 108 a that faces the internalinsulating member 12 and that is located on the back side of the currentcollector protrusion 108 x.

Modification 2

FIG. 15 is a bottom view of a sealing plate to which each component hasbeen attached in a prismatic secondary battery according to Modification2. FIG. 16 is a sectional view in the longitudinal direction of thesealing plate to which each component has been attached. FIG. 17 is anenlarged view illustrating the first positive electrode currentcollector, the second positive electrode current collector, the currentinterrupting mechanism, and the surrounding area in FIG. 16. Theprismatic secondary battery according to Modification 2 differs from theprismatic secondary battery according to Modification 1 in the shapes ofthe first positive electrode current collector, the second positiveelectrode current collector, and the first insulating member.

In Modification 2, a first positive electrode current collector 106 ahas a current collector protrusion 106 x in a region under a deformationplate 62 (a region adjacent to electrode body 3). A second positiveelectrode current collector 106 b has a tab connection region 106 b 1 towhich positive electrode tabs are connected, a linkage region 106 b 2extending downward (toward the electrode body 3) from an end of the tabconnection region 106 b 1, and a current collector connection region 106b 3 extending horizontally from an end of the linkage region 106 b 2.The current collector connection region 106 b 3 has a current collectoropening 106 y. The edge of the current collector opening 106 y isweld-connected to the current collector protrusion 106 x by means oflaser welding or the like. This configuration can reduce a spaceoccupied by the current collecting part.

The tab connection region 106 b 1 of the second positive electrodecurrent collector 106 b is disposed so as to face an insulating memberthird region 163 z of a first insulating member 163. The linkage region106 b 2 of the second positive electrode current collector 106 b isdisposed so as to face an insulating member second region 163 y of thefirst insulating member 163. The first positive electrode currentcollector 106 a is disposed so as to face an insulating member firstregion 163 x.

Like the first positive electrode current collector 6 a, the firstpositive electrode current collector 106 a has a thin portion 106 c. Thethin portion 106 c is weld-connected to the deformation plate 62. Acurrent collector second recess 106 w is formed in a surface of thefirst positive electrode current collector 106 a that faces the firstinsulating member 163 and that is located on the back side of thecurrent collector protrusion 106 x.

The second positive electrode current collector 106 b has a currentcollector first recess 106 f around the current collector opening 106 y.The second positive electrode current collector 106 b has an opening 106z at a position facing an electrolyte injection port 15 in the sealingplate 2. The first insulating member 163 has an insulating memberopening 163 b at a position facing the electrolyte injection port 15 inthe sealing plate 2. An insulating member protrusion 163 c protrudingdownward is disposed at the edge of the insulating member opening 163 b.

The prismatic secondary battery according to Modification 2 differs fromthe prismatic secondary battery 20 according to the embodiment in thepositions of fixation parts 70 at which the first insulating member 163is fixed to the first positive electrode current collector 106 a. In theprismatic secondary battery according to Modification 2, as illustratedin FIG. 16, two fixation parts 70 re aligned with each other in thetransverse direction of the sealing plate 2. The first insulating member163 in the prismatic secondary battery according to Modification 2differs from the first insulating member 63 in the prismatic secondarybattery 20 according to the embodiment in the position at which thefixation protrusion is formed.

Others

The embodiment is an example where the electrode body 3 is composed oftwo electrode body elements 3 a and 3 b, but the configuration is notlimited to this example. The electrode body 3 may be one stackedelectrode body. The electrode body 3 may be one wound electrode body inwhich a long positive electrode plate and a long negative electrodeplate are wound with a separator interposed therebetween. These twoelectrode body elements 3 a and 3 b are not necessarily stackedelectrode bodies and may be wound electrode bodies in which a longpositive electrode plate and a long negative electrode plate are woundwith a separator interposed therebetween.

The connection between the first positive electrode current collectorand the second positive electrode current collector and the connectionbetween the first negative electrode current collector and the secondnegative electrode current collector are preferably performed by meansof irradiation with an energy ray, such as a laser, an election beam,and an ion beam.

REFERENCE SIGNS LIST

20 Prismatic secondary battery

100 Battery case

1 Prismatic outer body

2 Sealing plate

-   -   2 a Positive electrode terminal attachment hole    -   2 b Negative electrode terminal attachment hole

3 Electrode body

-   -   3 a, 3 b Electrode body element

4 Positive electrode plate

-   -   4 a Positive electrode core    -   4 b Positive electrode active material mixture layer    -   4 d Positive electrode protective layer    -   40, 40 a, 40 b Positive electrode tab

5 Negative electrode plate

-   -   5 a Negative electrode core    -   5 b Negative electrode active material mixture laver.    -   50, 50 a, 50 b Negative electrode tab

6 a First positive electrode current collector

-   -   6 a 1 Current collector first region    -   6 a 2 Current collector second region    -   6 a 3 Current collector third region    -   6 c Thin potion    -   6 d Fixation through-hole    -   6 w Current collector second recess    -   6 x Current collector protrusion

6 b Second positive electrode current collector

-   -   6 b 1 Tab connection region    -   6 b 2 Current collector connection region    -   6 e Target hole    -   6 f Current collector first recess    -   6 y Current collector opening    -   6 z Opening    -   6A Stepped part

7 Positive electrode external terminal

-   -   7 a Terminal sealing member        -   7 x Metal plate        -   7 y Rubber member    -   7 b Terminal through-hole

8 a First negative electrode current collector

-   -   8 w Current collector second recess    -   8 x Current collector protrusion

8 b Second negative electrode current collector

-   -   8 b 1 Tab connection region    -   8 b 2 Current collector connection region    -   8 e Target hole    -   8 f Current collector first recess    -   8 y Current collector opening    -   8A Stepped part

9 Negative electrode external terminal

10 Internal insulating member

11 External insulating member

12 Internal insulating member

13 External insulating member

14 insulating sheet

15 Electrolyte injection port

16 Sealing plug

17 Gas release valve

60 Current interrupting mechanism

-   -   61 Conductive member    -   62 Deformation plate

63 First insulating member

-   -   63 a Fixation protrusion    -   63 b Insulating member opening    -   63 c Insulating member protrusion    -   63 x Insulating member first region    -   63 y Insulating member second region    -   63 z Insulating member third region

70 Fixation part

90 Weld-connected part

95 Welding jig

106 a First positive electrode current collector

-   -   106 c Thin portion    -   106 w Current collector second recess    -   106 x Current collector protrusion

106 b Second positive electrode current collector

-   -   106 b 1 Tab connection region    -   106 b 2 Linkage region    -   106 b 3 Current collector connection region    -   106 f Current collector first recess    -   106 y Current collector opening    -   106 z Opening

108 a First negative electrode current collector

-   -   108 w Current collector second recess    -   108 x Current collector protrusion

108 b Second negative electrode current collector

-   -   108 y Current collector opening    -   108 e Target hole    -   108 f Current collector first recess

163 First insulating member

-   -   163 b Insulating member opening    -   163 c Insulating member protrusion    -   163 x Insulating member first region    -   163 y Insulating member second region    -   163 z Insulating member third region

The invention claimed is:
 1. A method for producing a secondary battery including: an electrode body that includes a positive electrode plate and a negative electrode plate; an outer body that has an opening and houses the electrode body; a sealing plate that seals the opening; an external terminal that is attached to the sealing plate and inserted into a through hole of the sealing plate; a tab that is provided in the positive electrode plate or the negative electrode plate; and a first current collector and a second current collector that electrically connect the tab to the external terminal and that are disposed nearer a lower face of the sealing plate than an upper face of the sealing plate, wherein a connected portion of the first current collector with the external terminal is located nearer the lower face of the sealing plate than the upper face of the sealing plate, the method comprising: a fixation step of electrically connecting the first current collector to the external terminal and fixing the first current collector to the sealing plate; a first connection step of weld-connecting a stack of a plurality of the tabs to the second current collector; and a second connection step of connecting the first current collector to the second current collector after the fixation step and the first connection step.
 2. The method for producing a secondary battery according to claim 1, wherein the first connection step involves stacking 20 or more of the tabs on the second current collector and welding the tabs to the second current collector with the tabs and the second current collector sandwiched between welding jigs from two sides in a stacking direction of the tabs, and the second connection step involves welding the first current collector to the second current collector by means of irradiation with an energy ray.
 3. The method for producing a secondary battery according to claim 1, wherein the first connection step involves weld-connecting the tabs to the second current collector by means of ultrasonic welding or resistance welding.
 4. The method for producing a secondary battery according to claim 1, wherein the second current collector has a tab connection region substantially parallel to the sealing plate, and the tabs are weld-connected to the tab connection region.
 5. The method for producing a secondary battery according to claim 1, further comprising: an electrode-body-element-production step of producing a first electrode body element including the positive electrode plate and the negative electrode plate and a second electrode body element including the positive electrode plate and the negative electrode plate, wherein the first connection step involves placing the first electrode body element on one side of the second current collector, connecting the tabs of the first electrode body element to the second current collector, placing the second electrode body element on the other side of the second current collector, and connecting the tabs of the second electrode body element to the second current collector, and wherein the method further includes, after the second connection step, a step of combining the first electrode body element and the second electrode body element together into the electrode body and inserting the electrode body into the outer body.
 6. The method for producing a secondary battery according to claim 5, wherein, after the first electrode body element and the second electrode body element are combined together into the electrode body, and the electrode body is covered with an insulating sheet, the electrode body covered with the insulating sheet is inserted into the outer body.
 7. The method for producing a secondary battery according to claim 1, wherein the first current collector has a current collector protrusion, the second current collector has a current collector opening, and the second connection step involves inserting the current collector protrusion into the current collector opening and welding the current collector protrusion to an edge of the current collector opening.
 8. The method for producing a secondary battery according to claim 7, wherein an insulating member is disposed on a sealing plate side with respect to the first current collector, and a current collector recess is formed in a surface of the first current collector, the surface facing the insulating member and being located on a back side of the current collector protrusion.
 9. The method for producing a secondary battery according to claim 1, wherein the fixation step involves fixing an insulating member to the sealing plate, and the second connection step involves fixing the insulating member to the second current collector and then weld-connecting the first current collector to the second current collector.
 10. The method for producing a secondary battery according to claim 1, wherein the external terminal is a positive electrode external terminal, the tab is a positive electrode tab provided in the positive electrode plate, the first current collector is a first positive electrode current collector, the second current collector is a second positive electrode current collector, the secondary battery further includes: a negative electrode external terminal that is attached to the sealing plate and inserted into a through hole of the sealing plate; a negative electrode tab that is provided in the negative electrode plate; and a first negative electrode current collector and a second negative electrode current collector that electrically connect the negative electrode tab to the negative electrode external terminal and that are disposed nearer the lower face of the sealing plate than the upper face of the sealing plate, wherein a connected portion of the first negative electrode current collector with the negative electrode external terminal is located nearer the lower face of the sealing plate than the upper face of the sealing plate, and the method comprises: a first step of electrically connecting the first negative electrode current collector to the negative electrode external terminal and fixing the first negative electrode current collector to the sealing plate; a second step of weld-connecting a stack of a plurality of the negative electrode tabs to the second negative electrode current collector; and a third step of connecting the first negative electrode current collector to the second negative electrode current collector after the first step and the second step.
 11. The method for producing a secondary battery according to claim 10, wherein the second step involves stacking 20 or more of the negative electrode tabs on the second negative electrode current collector and welding the negative electrode tabs to the second negative electrode current collector with the negative electrode tabs and the second negative electrode current collector sandwiched between welding jigs from two sides in a stacking direction of the negative electrode tabs, and the third step involves weld-connecting the first negative electrode current collector to the second negative electrode current collector by means of irradiation with an energy ray.
 12. The method for producing a secondary battery according to claim 1, wherein a joined portion of the first current collector and the second current collector is located between the connected portion of the first current collector with the external terminal and a connected portion of the second current portion with the tab in a longitudinal direction of the sealing plate. 